A.c. powered surveillance system

ABSTRACT

A signaling apparatus having particular utility as a burglar alarm system is composed of a signaling circuit having an alarm signal source and a sensing circuit which trips the alarm source in the signaling circuit upon the appearance of a burglar or other condition to which the sensing circuit is sensitive. The sensing circuit includes a plurality of normally closed, serially connected switches which hold a sensing relay energized in the absense of the condition. With the appearance of the condition, the sensing relay is deenergized and a latching relay is tripped which energizes the alarm signal source. To prevent the latching relay from being tripped whenever power to the sensing relay is initially turned on or subsequently dips, a sequencing relay is interposed between the sensing relay and latching relay and insures that the sensing relay is energized first. Since the sensing relay is normally energized, there is continual supervision of the sensing circuit. The apparatus also has failsafe provisions and the signaling circuit is capable of providing a test signal each time the apparatus is turned on.

United States Patent [191 MacFarlane Oct. 16, 1973 A.C. POWEREDSURVEILLANCE SYSTEM [75] Inventor: John MacFarlane, Avon, Conn.

[73] Assignee: The Theodore D. Bross Line Construction Corporation,Bloomfield, Conn.

[22] Filed: May 3, 1971 [21] Appl. No.: 139,714

[52] US. Cl. 340/276, 340/274 [51] Int. Cl. G08b 13/08 [58] Field ofSearch 340/276, 274; 116/75, 86

[56] References Cited UNITED STATES PATENTS 3,200,393 8/1965 Worley340/276 2,493,576 l/l950 Foss 340/274 Primary Examiner-John W. CaldwellAssistant Examiner-Glen R. Swann, llI Attorney-McCormick, Paulding &Huber [5 7] ABSTRACT A signaling apparatus having particular utility asa burglar alarm system is composed of a signaling circuit having analarm signal source and a sensing circuit which trips the alarm sourcein the signaling circuit upon the appearance of a burglar or othercondition to which the sensing circuit is sensitive. The sensing circuitincludes a plurality of normally closed, serially connected switcheswhich hold a sensing relay energized in the absense of the condition.With the appearance of the condition, the sensing relay is deenergizedand a latching relay is tripped which energizes the alarm signal source.To prevent the latching relay from being tripped whenever power to thesensing relay is initially turned on or subsequently dips, a sequencingrelay is interposed between the sensing relay and latching relay andinsures that the sensing relay is energized first. Since the sensingrelay is normally energized, there is continual supervision of thesensing circuit. The apparatus also has fail-safe provisions and thesignaling circuit is capable of providing a test signal each time theapparatus is turned on.

15 Claims, 1 Drawing Figure PILOT LIGHT CRI 46 }L rom 3 MINUTE DELAY 50V 42 ALARM LIGHT A! /44 5 TDR L ALARM BEL 52 1 48 |a,-L l m L 24 I6 2626 2e SENSING RELAY CR1 so P Q SEQUENCING RELAY 28 V 34 32 5 3 36 QLATCHING RELAY W t CR 3 PATENIEDUBI 16 I915 3.766; 537

r PILOT LIGHT 3 MINUTE DELAY 5O 42 m I l ALARM LIGHT I SENSING RELAY (:Rso CW2 SEQUENCING RELAY 34 32 3s m A CR-3 LATCHING RELAY l INVENTOR.

JOHN MACFARLANE ATTORNEYS 1 A.C. POWERED SURVEILLANCE SYSTEM BACKGROUNDOF THE INVENTION The present invention relates to a signaling apparatuswhich provides a visual, audio or other type of signal upon thedetection of a condition to which the apparatus is sensitized. Theapparatus is specially suited to the function of a burglar alarm systemand has self-testing and continual supervision features.

In apparatus which is designed to detect a particular condition thatoccurs with random or unscheduled frequency over extended periodsoftime, it is desirable that the systems be continually supervised andfail-safe. It is also desirable that such systems not require extensivemaintenance or frequent servicing during the period of activation. Thespecifications that a system be continually supervised and, at the sametime, not require frequent servicing are, for practical purposes,conflicting prerequisites; however, these prerequisites are frequentlydemanded in many types of warning systems, especially in burglar alarmsystems which lie dormant for long periods of time and yet must beprepared to give an alarm signal when the security of the area undersupervision is first broken.

In many burglar alarm systems, it is customary to employ batteries forenergizing the system. While batteries provide a reliable source ofelectrical power on a short term basis, they must be recharged orreplaced on occasion for extended reliability of the system. Wherereasonably reliable line power is available, the maintenance aspects ofthe battery-operated systems can be eliminated.

Where it is desired to combine the continual supervision feature withthe low maintenance feature in an alarm system, reliable line power isalso an attractive alternative as a power source because continualsupervision normally requires continual energization of a sensingcircuit. In systems utilizing batteries, the continual energizationresults in a more rapid discharge of the batteries. If the sensingcircuit is not continually energized so that power consumption isavoided, the supervision or monitoring features of the system are lost.It is therefore desirable to utilize line power for a burglar alarmwhere low maintenance and continual supervision features are desired.

One problem associated with line power in a supervised alarm system isthat the system must be capable of discriminating between the actualdetection of a condition to which the system is sensitive and a powerfailure or fluctuation in the voltage level of the power since bothsituations are accompanied by loss of energization in the sensingcircuits. Only the former situation, the actual detection, should setoff the alarm.

Accordingly, it is a general object of the present invention to providea signaling apparatus having low maintenance, fail-safe and supervisoryfeatures and which at the same time can distinguish between thedetection of a selected condition and a power failure.

SUMMARY OF THE INVENTION The present invention resides in a signalingapparatus comprised of an electrical sensing circuit and signalingcircuit. The sensing circuit has a normally closed sensing switchsensitive to and opened by a condition to be detected and a sensingmeans connected with and electrically energized through the sensingswitch. The signaling circuit is provided with an alarm signal sourcesuch as a light or alarm bell which is actuated by the sensing circuitwhen the sensing switch is opened and the sensing means is de-energized.Latching means is connected between the sensing means. and the alarmsignal source and is responsive to the sensing means for actuating thealarm signal source subsequent to the deenergization of the sensingmeans. Sequencing means is provided for arming the latching means afterenergization of the sensing means and prevents the latching means fromtripping the alarm signal source when the signaling apparatus is firstturned on by switch means electrically connected with the signaling andsensing circuits.

The sequencing means is utilized to provide a test signal each time thesignaling apparatus is energized. The energization of the sensing meansthrough the normally closed sensing switches provides continualmonitoring or supervision of the signaling apparatus and the alarmsignal source is actuated upon a failure of either the sensing means orsequencing means. The signaling apparatus, therefore, has testing,monitoring and fail-safe features.

BRIEF DESCRIPTION OF THE DRAWING The drawing is an electrical diagramshowing the signaling and sensing circuits of a preferred embodiment ofthe signaling apparatus of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The signaling apparatus of thepresent invention having testing, monitoring and fail-safe features isshown in the drawing in a preferred embodiment. While the invention issuitable for other uses, the signaling apparatus has particularlyutility as a burglar alarm system and hence is shown in the drawing anddescribed below in such a form to more clearly present its severalfeatures.

The signaling apparatus, generally designated 10, is energized by apower source 12 which in its most common form would be a 110 volt or 220volt ac power supply line such as that found in most buildings or areaswhich are secured by an alarm system. The signaling apparatus 10 iscomprised of a high voltage signaling circuit 14 connected to the powersupply 12 and a low voltage sensing circuit 16 coupled to the signalingcircuit 14 by means of an ac step-down transformer 18. The transformerreduces the excitation voltage of the signaling circuit to, for example,24 volts across the secondary winding which excites the sensing circuit16. A master control switch 20 in the high voltage circuit 14 isutilized to turn the signaling apparatus 10 on and off by connecting thepower source 12 directly to the signaling circuit 14 and indirectly tothe sensing circuit 16 through the transformer 18. As shown, the controlswitch 20 is a single-pole,single-throw switch 20 which may be keyoperated so that the system can be either locked on or off by securitypersonnel. The switch 20 serves as the only manual control for the alarmsystem and consequently all other features of the system such astesting, monitoring and signaling failures are automatically controlled.

With the control switch 20 closed, a pilot light 22 is energized toindicate that the signaling apparatus 10 is turned on. In thiscondition, power is transmitted through the transformer 18 to the lowvoltage sensing circuit 16 and energizes a sensing relay 24, designatedCR-l, through a plurality of serially connected sensing switches 26. Thesensing switches 26 are normally closed and so arranged in a building asto be opened in the presence of a condition to be detected. For example,in the burglar alarm system, the switches 26 are actuated to the openposition whenever a door or window of a building is opened. It will thusbe apparent that the switches 26 may be mechanically actuated by awindow or a door, or that other devices such as photoelectric cells andsimilar detection devices might be used. The term sensing switch isintended to cover such devices.

With each of the sensing switches 26 in the closed position indicating asecure condition, the sensing relay 24 is energized. The relay 24 isprovided with a set of normally open contacts 28 which are connected inseries with a sequencing relay 30 designated CR-2. When the sensingrelay 24 is energized, contacts 28 close and energize the sequencingrelay 30. The sequencing relay 30 has a pair of normally open, latchingcontacts 32 which close upon energization of the sequencing relay tohold the sequencing relay in the energized condition after it isintially energized through the contacts 28. The contacts 32 areconnected in series with a latching relay 34, designated CR-3, through aset of normally closed contacts 36 forming a part of the sensing relay24. The contacts 32 of the sequencing relay 30 serve the function ofarming the latching relay 34 subsequent to the energization of thesensing relay 24 through the switches 26.

During power up operations, the sensing relay 24 is energized first andin turn closes contacts 28 and opens contacts 36; contacts 28 and 36being transfer contacts whereby contacts 36 must open before contacts 28close. The sequencing relay 30 is not energized until after the sensingrelay has been energized and therefore contacts 36 are opened beforecontacts 32 are closed. Accordingly, the latching relay 34 is notenergized when power is first turned on due to the delayed response ofthe sequencing relay contacts 32.

During normal operation (power on), the deenergization of the sensingrelay 24 due to the opening of one of the sensing switches 26 permitscontacts 36 to return to a closed position to energize the latchingrelay 34. The relay 34 has one set of latching contacts 38 which holdrelay 34 energized after one of the sensing switches 26 is opened andanother set of normally opened contacts 40 connected in the high voltagesignaling circuit 14 in series with an alarm signal source such as thealarm light 42 or the alarm bell 44. Consequently, whenever a sensingswitch 26 is opened during power on operation, contacts 38 and 40 oflatching relay 34 close and the alarm signal source is energized. Thealarm signal source remains energized even though the sensing switchwhich caused the contacts 40 to close is returned to its normally closedposition. It will be apparent therefore, that even if a burglar realizesthat he has set off the alarm signal, he cannot deenergize the alarmsource by reclosing the switch 26 since the relay 34 is latched bycontacts 38.

The alarm light 42 and the alarm bell 44 are connected in parallel witheach other and with a time-delay relay 46 and all of these devices areenergized by the contacts 40. The time-delay relay 46 has a set ofnormally closed contacts 48 connected in series with the alarm bell 44and after the relay is energized for a delay period of, for example,three minutes, the contacts 48 open and de-energize the alarm bell 44.The time-delay relay 46 thereby permits the alarm bell 44 to provide analarm sound of sufficient duration to warn security personnel that aburglar has tripped one of the sensing switches 26. The bell then shutsoff, but the alarm light 42 remains energized to provide a continuousvisual indication that the signaling apparatus has been tripped.

The signaling apparatus 10 is shut off and reset by opening and closingthe key control switch 20. When the switch 20 is opened, the sensingrelay 24, the sequencing relay 30 and the latching relay 34 aredeenergized in conjunction with the alarm light 42 and alarm bell 44. Atthis point, all of the elements of the signaling and sensing circuitsare returned to the original conditions observed prior to power-upoperations. Consequently, when the control switch 20 is reclosed,sensing relay 24 and sequencing relay 30 are reenergized in that orderand arm the latching relay 34 as described above.

The above description details the normal operation of the signalingapparatus in detecting an unauthorized entry or breaking into a securedarea. The automatic testing and supervising functions performed by thesignaling apparatus 10 will now be described.

The signaling apparatus 10 automatically provides a test signal eachtime the control switch 20 is closed or power is reapplied to thesignaling apparatus. The test signal consists of a momentary operationof the alarm light 42 and the alarm bell 44, and if the apparatus isworking properly, the alarm bell and alarm light are shut off after themomentary operation. If the signaling apparatus is not working properly,the alarm bell and alarm light continue to operate and thereby indicatea failure within the apparatus.

As mentioned above, the alarm light 42, the alarm bell 44,and thetime-delay relay 46 are all turned on by the normally open contacts 40of the latching relay 34 when the sensing switches 26 are opened. Inaddition, however, a set of normally closed contacts 50 forming a partof the sensing relay 24 and another set of normally closed contacts 52forming a part of the sequencing relay 30 are connected in parallel withthe contacts 40 and each of these is also capable of energizing thealarm light and alarm bell. Before power is applied to the signalingcircuit 14 and sensing circuit 16 through the control switch 20, neitherthe sensing relay 24 nor the sequencing relay 30 is energized andtherefore contacts 50 and 52 are in the normally closed positions. Whenthe switch 20 is closed, power is applied to both the alarm light 42 andthe alarm bell 44 until the sequencing relay 30 is energized to opencontacts 52 since the energization of the sequencing relay 30 is delayedby the normally open contacts 28 of the sensing relay 24. During thisbrief delay the alarm light 42 remains on and the alarm bell 44 issounded to indicate to security personnel that the apparatus isoperative.

If for any reason the sensing relay 24 fails to operate, contacts 50remain closed, the alarm light continues to burn and the alarm bellrings until the time-delay relay 46 opens contacts 48. Similarly, if thesequencing relay 30 fails to operate, contacts 52 remain closed and thealarm light and the alarm bell continue to function beyond the momentarytest period normally provided by the sequencing relay 30. The signalingapparatus, therefore, automatically provides its own test signal eachtime the control switch 20 is closed or whenever power is returned tothe signaling and sensing circuits.

The signaling apparatus also monitors itself after it is turned on andprovides a warning signal through the alarm light 42 or alarm bell 44 inthe event that a failure occurs in one of the components. The apparatus10, therefore, supervises itself after power is turned on and fails safeor gives a break indication by energizing the alarm signal source.

To provide these supervising and fail-safe features after the apparatusis turned on and the testing operation is completed, the sensing relay24 is continuously energized through the normally closed sensingswitches 26 and the sequencing relay 30 is continuously energizedthrough the contacts 28. If for any reason the sensing relay 24 fails,the contacts 50 close and energize the alarm sources 42 and 44 toindicate the failure. The alarm sources, therefore, provide securitypersonnel with an indication that the system is not operating properlyby providing a break indication when the sensing relay fails; theindication being in the form of a stored signal as provided by light 42and an audible warning provided by alarm 44 and being of durationdetermined by time delay relay 46.

In the same manner, if the sequencing relay 30 fails, the contacts 52close and energize the alarm light and bell. It should also be notedthat a failure of the transformer 18 results in the de-energization ofboth the sensing relay 24 and the sequencing relay 30 so that an alarmis sounded in this case as well. A failure of the latching relay 34 doesnot produce an immediate warning signal; however, the apparatus with afailed latching relay will continue to operate and produce a warningsignal whenever a sensing switch 26 is opened since the de-energizationof the sensing relay 24 closes the set of contacts 50 which energize thealarm signal source. Thus, when the latching relay 34 fails, only thelatching feature of the alarm system is lost. The result is that anintruder who recloses one of the opened sensing switches can shut offthe alarm signal.

It will thus be seen that the signaling apparatus 10 provides an alarmsignal whenever one of the sensing switches 26 is opened and theapparatus has both testing, supervising and fail-safe features. Thetesting feature is automatically provided each time the apparatus isenergized and does not require a special testing switch. The supervisingfeature is also automatic and the apparatus does not sound the alarmafter a power failure because the sequencing relay renders the apparatuscapable of distinguishing between the opening of a sensing switch and afailure of the power source. Due to the capability of distinguishingbetween such conditions, itis possible to employ 'a simple single-pole,single-throw switch for activating and deactivating the signalingapparatus.

While the signaling apparatus has been described in a preferredembodiment, it should be understood that various modifications andsubstitutions can be had without departing from the spirit of theinvention. For example, although the sequencing relay is operated by thesensing relay contacts 28 to provide a delayed signal for arming thelatching relay 34, the relay 30 could be replaced by a time-delay relayconnected directly across the secondary winding of the transformer 18without employing the sensing relay contacts 28 or the latchingcharacteristics of the relay 30. In addition, the sequencing relay 30and the latching relay 34 together with contacts 28, 32, 36, 38 need notbe operated at low voltage in the sensing circuit 16 but might belocated in the signaling circuit 14 and operated at normal supplyvoltages. Although the sensing circuit i6 is shown to operate on acpower from the transformer 18, the transformer could be eliminated or anac-to-dc converter could be utilized in place of the transformer so thatthe sensing circuit 16 could operate on direct current. Accordingly, thepresent invention has been described in a preferred embodiment by way ofillustration rather than limitation.

I claim:

1. A surveillance system comprising:

condition responsive means, said condition responsive means including atleast first switch means, said first switch means changing state uponestablishment of a predetermined condition in an area undersurveillance;

electrical power supply means;

means for energizing the system by connecting said power supply meansthereto;

sensing means responsive to the state of said condition responsivemeans, said sensing means includ-v ing first solenoid operated relaymeans having a plurality of contacts, the solenoid of said first relaymeans being energized from said power supply means through said firstswitch means;

alarm means;

latching means for supplying current from said power supply means tosaid alarm means, said latching means being energized via a first pairof contacts of said sensing means first relay means; and self-latchingsequencing means for arming said latching means, said sequencing meansbeing energized from said power supply means via a second pair ofcontacts of said first relay means and establishing a circuit betweensaid power supply means and a first contact of said first pair ofsensing means first relay means contacts whereby the change of state ofsaid first switch means will change the energization state of saidsensing means first relay means only to cause energization of said alarmmeans via said armed latching means and whereby a momentary interruptionof power from said power supply means will cause deenergization of saidsequencing means and said alarm means will not be energized uponresumption of the application of power.

2. The surveillance system of claim 1 wherein said sensing means firstrelay means is energized through said first switching means uponconnection of the system to the power supply means and wherein saidsequencing means is energized to arm said latching means subsequent toenergization of said sensing means.

3. The surveillance system of claim 2 further comprising:

first actuating means for said alarm means, said first actuating meansapplying power to said alarm means upon operation of said energizingmeans to connect power to the system, said first actuating means beingresponsive to energization of said se quencing means for disrupting thesupply of power from said power supply means to said alarm means.

4. The surveillance system as defined in claim 3 wherein the sequencingmeans comprises a sequencing relay having a first set of contactsconnected with the latching means and normally open in the deenergizedstate of the sequencing relay; and wherein said first actuating meanscomprises a second set of contacts in the sequencing relay, the secondset of sequencing relay contacts being normally closed in thedeenergized state of the sequencing relay.

5. The surveillance system as defined in claim 2 wherein said alarmmeans includes alarm signal generating means and first and second setsof alarm signal generating means energizing contacts, each set of alarmsignal generating means energizing contacts being connected with thealarm signal generating means and being connected in parallel with eachother, the first set of alarm signal generating means energizingcontacts being closed by the deenergization of the sensing means and thesecond set of alarm signal generating means energizing contacts beingclosed by the energization of the latching means.

6. The surveillance system as defined in claim 5 wherein the alarm meansfurther includes a third set of contacts connected in parallel with thefirst and second sets of alarm signal generating means energizingcontacts, the third set of contacts being opened by the sequencing meanswith the arming of the latching means.

7. The surveillance system as defined in claim 6 wherein the sensingmeans is a relay including the first set of alarm signal generatingmeans energizing contacts; the latching means is a latching relayincluding the second set of alarm signal generating means energizingcontacts and the sequencing means is a relay including said third set ofcontacts.

8. A signaling apparatus comprising:

an electrical sensing circuit having a normally closed sensing switchsensitive to and opened by a condition to be detected and sensing meansconnected with and electrically energized through the sensing switch;

a signaling circuit having an alarm signal source;

latching means connected between the sensing means and the alarm signalsource and responsive to deenergization of the sensing means foractuating the alarm signal source in the signaling circuit subsequent toa deenergization of the sensing means;

switch means electrically connected with the signaling and sensingcircuits for energizing the circuits; and

sequencing means connected to and responsive to the sensing means forarming the latching means subsequent to the energization of the sensingmeans.

9. A signaling apparatus as defined in claim 8 wherein the sequencingmeans comprises a relay responsive to the sensing means and having a setof latching contacts.

10. A signaling apparatus as defined in claim 8 wherein the latchingmeans comprises a latching relay.

11. A signaling apparatus as defined in claim 8 wherein the switch meansconsists of a single-pole, single-throw switch connected to thesignaling circuit and the sensing circuit.

12. A signal apparatus as defined in claim 8 wherein the signal circuitis a high voltage circuit and the sensing circuit is a low voltagecircuit and wherein power transfer means is connected between the signaland sensing circuits.

13. A burglar alarm apparatus comprising:

an alarm signal circuit having an alarm signal source;

a sensing circuit having at least one normally closed sensing switch anda sensing relay energized through the sensing switch, the sensing relayhaving at least one set of normally closed contacts; single-throwcontrol switch connected to energize each of the circuits from anelectrical power source; sequencing relay connected in one of thecircuits and having a first set of normally closed contacts and a secondset of normally open contacts, said first set of sequencing relaynormally closed contacts being connected serially in the signalingcircuit with the alarm signal source, the first and second sets ofsequencing relay contacts being actuated by the sequencing relay in asequence with and subsequent to the energization of the sensing relay inthe sensing circuit; and

a latching relay armed by the second set of normally opened contacts ofthe sequencing relay and serially connected in one of the circuits withthe said one set of normally closed contacts of the sensing relay, thelatching relay also having a set of normally open contacts connectedserially with the alarm signal source and in parallel with the normallyclosed contacts of the sequencing relay.

14. A burglar alarm apparatus as defined in claim 13 wherein the sensingrelay includes a set of normally open contacts serially connected in oneof the circuits with the sequencing relay and a second set of normallyclosed contacts connected serially with the alarm signal source in thesignaling circuit and in parallel with the normally open contacts of thelatching relay and the normally closed contacts of the sequencing relay.

15. A burglar alarm apparatus as defined in claim 13 wherein a timedelay relay having a set of normally closed contacts connecting thealarm signal source in series with the normally open contacts of thelatching relay and in series with the normally closed contacts of thesequencing relay is connected in the alarm signal circuit in parallelwith the alarm signal source and contacts of the time delay relay.

1. A surveillance system comprising: condition responsive means, said condition responsive means including at least first switch means, said first switch means changing state upon establishment of a predetermined condition in an area under surveillance; electrical power supply means; means for energizing the system by connecting said power supply means thereto; sensing means responsive to the state of said condition responsive means, said sensing means including first solenoid operated relay means having a plurality of contacts, the solenoid of said first relay means being energized from said power supply means through said first switch means; alarm means; latching means for supplying current from said power supply means to said alarm means, said latching means being energized via a first pair of contacts of said sensing means first relay means; and self-latching sequencing means for arming said latching means, said sequencing means being energized from said power supply means via a second pair of contacts of said first relay means and establishing a circuit between said power supply means and a first contact of said first pair of sensing means first relay means contacts whereby the change of state of said first switch means will change the energization state of said sensing means first relay means only to cause energization of said alarm means via said armed latching means and whereby a momentary interruption of power from said power supply means will cause deenergization of said sequencing means and said alarm means will not be energized upon resumption of the application of power.
 2. The surveillance system of claim 1 wherein said sensing means first relay means is energized through said first switching means upon connection of the system to the power supply means and wherein said sequencing means is energized to arm said latching means subsequent to energization of said sensing means.
 3. The surveillance system of claim 2 further comprising: first actuating means for said alarm means, said first actuating means applying power to said alarm means upon operation of said energizing means to connect power to the system, said first actuating means being responsive to energization of said sequencing means for disrupting the supply of power from said power supply means to said alarm means.
 4. The surveillance system as defined in claim 3 wherein the sequencing means comprises a sequencing relay having a first set of contacts connected with the latching means and normally open in the deenergized state of the sequencing relay; and wherein said first actuating means comprises a second set of contacts in the sequencing relay, the second set of sequencing relay contacts being normally closed in the deenergized state of the sequencing relay.
 5. The surveillance system as defined in claim 2 wherein said alarm means includes alarm signal generating means and first and second sets of alarm signal generating means energizing contacts, each set of alarm signal generating means energizing contacts being connected with the alarm signal generating means and being connected in parallel with each other, the first set of alarm signal generating means energizing contacts being closed by the deenergization of the sensing means and the second set of alarm signal generating means energizing contacts being closed by the energization of the latching means.
 6. The surveillance system as defined in claim 5 wherein the alarm means further includes a third set of contacts connected in parallel with the first and second sets of alarm signal generating means energizing contacts, the third set of contacts being opened by the sequencing means with the arming of the latching means.
 7. The surveillance system as defined in claim 6 wherein the sensing means is a relay including the first set of alarm signal generating means energizing contacts; the latching means is a latching relay including the second set of alarm signal generating means energizing contacts and the sequencing means is a relay including said third set of contacts.
 8. A signaling apparatus comprising: an electrical sensing circuit having a normally closed sensing switch sensitive to and opened by a condition to be detected and sensing means connected with and electrically energized through the sensing switch; a signaling circuit having an alarm signal source; latching means connected between the sensing means and the alarm signal source and responsive to deenergization of the sensiNg means for actuating the alarm signal source in the signaling circuit subsequent to a deenergization of the sensing means; switch means electrically connected with the signaling and sensing circuits for energizing the circuits; and sequencing means connected to and responsive to the sensing means for arming the latching means subsequent to the energization of the sensing means.
 9. A signaling apparatus as defined in claim 8 wherein the sequencing means comprises a relay responsive to the sensing means and having a set of latching contacts.
 10. A signaling apparatus as defined in claim 8 wherein the latching means comprises a latching relay.
 11. A signaling apparatus as defined in claim 8 wherein the switch means consists of a single-pole, single-throw switch connected to the signaling circuit and the sensing circuit.
 12. A signal apparatus as defined in claim 8 wherein the signal circuit is a high voltage circuit and the sensing circuit is a low voltage circuit and wherein power transfer means is connected between the signal and sensing circuits.
 13. A burglar alarm apparatus comprising: an alarm signal circuit having an alarm signal source; a sensing circuit having at least one normally closed sensing switch and a sensing relay energized through the sensing switch, the sensing relay having at least one set of normally closed contacts; a single-throw control switch connected to energize each of the circuits from an electrical power source; a sequencing relay connected in one of the circuits and having a first set of normally closed contacts and a second set of normally open contacts, said first set of sequencing relay normally closed contacts being connected serially in the signaling circuit with the alarm signal source, the first and second sets of sequencing relay contacts being actuated by the sequencing relay in a sequence with and subsequent to the energization of the sensing relay in the sensing circuit; and a latching relay armed by the second set of normally opened contacts of the sequencing relay and serially connected in one of the circuits with the said one set of normally closed contacts of the sensing relay, the latching relay also having a set of normally open contacts connected serially with the alarm signal source and in parallel with the normally closed contacts of the sequencing relay.
 14. A burglar alarm apparatus as defined in claim 13 wherein the sensing relay includes a set of normally open contacts serially connected in one of the circuits with the sequencing relay and a second set of normally closed contacts connected serially with the alarm signal source in the signaling circuit and in parallel with the normally open contacts of the latching relay and the normally closed contacts of the sequencing relay.
 15. A burglar alarm apparatus as defined in claim 13 wherein a time delay relay having a set of normally closed contacts connecting the alarm signal source in series with the normally open contacts of the latching relay and in series with the normally closed contacts of the sequencing relay is connected in the alarm signal circuit in parallel with the alarm signal source and contacts of the time delay relay. 